To meet the strict transient requirements of future microprocessors and to reduce the number of passive components required to achieve high power density, the switching frequency of voltage regulators (VR) will move into the megahertz (MHz) range in the next few years [1]-[4].
However, an increase in switching frequency may lead to poor efficiency of the VR due to excessive switching loss and gate drive loss, which are proportional to the switching frequency. Consequently, overall performance of the VR will be degraded. More importantly, it has been shown that in applications such as a high frequency (1 MHz) synchronous buck VR, the parasitic inductance, especially the common source inductance, has a substantial propagation effect during the switching transition of the power switching devices and thus results in high switching loss [5].
The resonant gate drive technique has received considerable attention as an approach to recovering gate energy lost in conventional gate drivers. In the approach taken by Chen et al. [6], the power MOSFET gate was not actively clamped high or low, which resulted in poor noise immunity. Yao et al. proposed resonant drivers using a coupled inductor [7] or a transformer [8] that were able to drive two MOSFETs. However, the leakage inductance of these approaches becomes substantial at MHz frequency. A full-bridge topology drive circuit with one inductor to drive two ground-sharing MOSFETs in a 1 MHz Boost converter was proposed by Li et al. [9]. Dwane et al. [10] provided an assessment of resonant drive techniques for use in low power dc/dc converters, and Lopez et al. [11] constructed a mathematical model to estimate the power loss of a resonant drive circuit. However, all of these approaches focus on gate energy savings realized by the resonant gate driver, but do not consider the potential switching loss savings, which are more important in a VR and other switching converters operating at MHz frequencies.
In our previous work [12]-[16], we showed that use of a constant drive current in a resonant gate driver can significantly reduce the switching transition time and switching loss of power switching devices. Using a current-source topology for the driver in a buck VR, we demonstrated a significant improvement in efficiency over the conventional voltage driver at a switching frequency of 1 MHz. However, with that approach it was not possible to achieve control of the power switching devices independently.